This invention relates to a better method and means of measuring the fuel content of a quantity of nuclear fuel containing plutonium or other heat-producing constituents.
A prime objective of the Nuclear Safeguards Program is the continual measured control of the inventory of fissionable materials, especially plutonium, that is in the form of fuel rods ready for insertion into nuclear reactors. In addition to the pressing concern for maintaining tight control of a plutonium inventory against possible theft, it is desirable for operating purposes to know that state of an inventory of fuel rods. Furthermore, it is desirable to be able to measure a given nuclear fuel rod to assure that the rod has been properly loaded with an appropriate number of fuel pellets of a desired activity. In addition, it may be desirable to measure a single pellet, and it may be desirable to measure quantities of fuel in other forms, such as plates or slurries. All these objectives can be achieved best by a method or means of measuring nondestructively the radioactivity of a quantity of fuel that is convenient to the places where the fuel is either manufactured or stored before use. It is also necessary that such measurements be made on schedules approximating a production basis in a reasonable length of time.
One method of assessing the activity of nuclear fuel comprises measuring the radiation emitted from this fuel in the form of alpha, beta, or gamma radiation or neutrons or a combination thereof. The spectra thus determined are useful in determining the types of radioactive materials in the fuel and the intensities thus determined can be interpreted to give information about the quantities of materials on hand. However, this method does not provide sufficient accuracy to satisfy all the needs of a program of nuclear safeguards and it is sufficiently time-consuming to be of questionable value even for operating inventory control. The highest accuracy is achieved by a combination of chemical and mass-spectrometric analyses, but these are of necessity destructive tests. Calorimetric methods have been used to measure the heat emitted by nuclear fuel and to provide information on the quantities of radioactive material in combination with information obtained by spectrometric analysis or by previous chemical analysis as to the expected constituents in the fuel. However, calorimetric methods providing sufficient accuracy in measuring nuclear fuel rods or pellets for the nuclear safeguards program have heretofore involved the use of large liquid calorimeters in closely controlled laboratory measuring situations. These methods also have taken considerable lengths of time, periods of the order of hours for each fuel rod, which obviates their use for routine methods of inventory control on something approximating a production basis. It would be conceivable to transport a substantial inventory of fuel rods to a remote location for calorimetric measurement, but such an exercise would be futile if the measurements took hours for each fuel rod.
It is an object of the present invention to provide a better method and means of analyzing nuclear fuel nondestructively.
It is a further object of the present invention to provide a fast, accurate, portable instrument for measuring the fuel content of nuclear fuel pellets.
It is a further object of the present invention to provide a fast, accurate, portable instrument for measuring the fuel content of nuclear fuel rods.
It is a further object of the present invention to provide a fast, portable dry calorimeter for nondestructive analysis of the quantities of radioactive materials present in samples of nuclear fuel.
Other objects will become apparent in the course of a detailed description of the invention.